The present invention relates to a method for soldering the core end of an electrical wire to a contact terminal of a connector by means of a soldering sleeve, said soldering sleeve being a shrinkable tube including meltable soldering material, and said method comprising the steps of:
positioning said core end onto said contact terminal; PA1 positioning said soldering sleeve so as to cover said core end and said contact terminal; and PA1 heating said soldering sleeve in order to melt the soldering material included therein and so to solder said core end to said contact terminal. PA1 a pre-soldering fool with pressure means adapted to press said core end and said contact terminal together, and with electrical means adapted to provide an electrical current flowing via said joint core end and contact terminal, so as to pre-solder them together according to the soldering by resistance method; and PA1 an inductive soldering tool adapted to heat by induction said soldering sleeve covering the pre-soldered core end and contact terminal in order to melt the soldering material included in said soldering sleeve and to shrink the shrinkable tube.
Such a method is already known in the art, e.g. from "Operating and Maintenance Manual" of the AA-400 Super Heater-Mark III heating gun of the Raychem Corporation.TM.--Electronics Group, located at 300 Constitution Drive, Menlo Park--Calif. 94025. Therein is described the above method that consists of positioning, by an operator, the electrical wire on a positioning tool in order to bring the core end of the wire into contact with the contact terminal while covering the whole with the shrinkable soldering sleeve. At the same time, the operator heats the soldering sleeve with a heating gun. By this heating, the solder of the sleeve melts and provides a soldered connection between the contact terminal and the core end of the wire. Secondly the sleeve shrinks over the soldered connection.
In this known method, the positioning of the core end of the wire onto the contact terminal must be very precise and, because it is covered by the soldering sleeve and thus no longer visible, it is very difficult for an operator to maintain this position during the whole soldering process. The result is thus very dependent of the ability and experience of the operator.
The quality of the resulting soldered connection and of the shrinked down sleeve is also very much influenced by the human factor. Indeed, the heating with a heating gun is a relatively long and fastidious operation during which it is not easy to obtain a uniform heat. Generally only the side near to the gun gets the necessary calories to heat the connection. This is particularly true with hot air guns that also have the particularity that the heating resistors thereof degrade slowly whereby, as result, it becomes rapidly harder to get the same result even if the gun is still in the calibration tolerance. As a consequence, the operator has to adapt to the changing performance of the heating gun.